How are convection currents produced in the air?

Convection currents are caused by the colliding of cold and warm air. At night, air above water is warm and air above land is cold. The opposite is true in daytime. When the warm air hits the cold air, which is more dense, it is pushed upward. Then it travels laterally until it cools. It comes back down and pushes up the former cold air, which is now warm. This repeats many times.